Tìm X

* Hướng dẫn giải

$$\begin{gathered} a) x: \frac{3}{4}=\frac{2}{5} \\ x=\frac{2}{5}\times \frac{3}{4} \\ x= \frac{6}{10} \\ x= \frac{3}{10} \end{gathered}$$                                 $$\begin{gathered} b) x\times \frac{3}{7}=\frac{6}{5} \\ x= \frac{6}{5}: \frac{3}{7} \\ x= \frac{6}{5}\times \frac{7}{3} \\ x= \frac{42}{15} \\ x= \frac{14}{5} \end{gathered}$$